A convergent strategy is proposed to increase the therapeutic potential of antisense compounds that target the erbB2 receptor which is overexpressed in 30 percent of breast cancers and appears casually related to the cancer phenotype. In this dual approach, the synthetic chemistry and biological applications of a group of novel oligomer carrier macromolecules termed dendrimers will be investigated. In complement to the development of these delivery systems new promising chemistries will be investigated to produce maximal antisense potency while minimizing toxicity. Two novel classes of dendrimers will be synthesized. One class of dendrimers, a carboxylic ester linked phosphazene core dendrimer, will be designed to slowly degrade after entry into the cell into nontoxic metabolites. A second class of dendrimers will be constructed of partly antisense DNA and assembled by hybridization of complementary single stranded trimers of DNA linked to phosphazene cores. The serum stability, cellular uptake, toxicity, and capacity for delivering antisense oligomers will be studied in breast cancer cell systems. An effort will be made to design dendrimers that escape endosome containment. In particular the fusogenic influenza virus peptide, HA2, will be presented to cells concentrated on the surface of dendrimers. Direct evaluations of the capacity of dendrimers to deliver oligomers into cells will be monitored by observing the appearance of fluorescein tagged oligmers within cell nuclei by confocal microscopy. In addition, new synthetic versions of the lead anti-erbB2 antisense compound-US-3 will be tested for antisense efficacy. Significant advances in the solid phase chemistry of boranophosphates will allow high purity boronated US-3 and C2 control compounds to be tested in cells,. Novel low charged chimeric methylphosphonate compounds with charged cores of either boranophosphonate or alternating phosphorodithioate/phosphodiester backbones will be made and antisense potency evaluated with flow cytometric and microinjection strategies.